When Is a Good Time to Weed Spray Your Lawn?

By Kelli Bingham ; Updated September 21, 2017

The best time to weed spray your lawn depends on the type of herbicide you will use. Pre-emergence herbicides control germinating seeds, and you should spray two or three weeks before weeds have germinated. Post-emergence herbicides control weeds that have already grown in. You should spray these when weed plants are young.